P-Cells and I-Cells in in Vitro Slices of the Lateral Geniculate Nucleus of the Cat

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Abstract
Extra- and intracellular recordings were performed from neurons in in vitro slices of the lateral geniculate nucleus (LGN) prepared from cats anesthetized with Nembutal. Based on responses to stimulation of the optic tract (OT), neurons were classified into 3 types, i.e., P-cells (principal relay cells), I-cells (intrinsic cells) and unclassified cells. P-cells were characterized by an inhibitory post-synaptic potential following excitatory post-synaptic potential [EPSP] or an action spike which appeared at a short latency in response to OT stimulation, while I-cells were characterized by a long-lasting EPSP on which a burst of spikes were superimposed. These observations were comparable with those reported in situ. The incidence of P- and I-cells was investigated for 118 neurons recorded intracellularly from in vitro slices of LGN of cats at various ages; 73.0% and 5.4% for P- and I-cells, respectively, in 1 day old kittens, 71.4 and 9.5% in 3 day old, 81.8 and 9.1% in 1 wk old, 80.8 and 7.7% in 6 wk old kittens and 82.6 and 13.0% in adult cats. Apparently physiologically differentiated P- and I-cells exist in the LGN even at birth and I-cells are responsible for intrageniculate inhibition.